Universal joint with protective shield

ABSTRACT

A constant velocity (CV) joint includes a shield to protect a J-boot from damage due to projectiles such as stones and to prevent ballooning. A rigid portion of the shield is fixed to a ring, which is adapted for fixation to a powertrain component such as a transmission. A flexible portion of the shield prevents projectiles from entering through the opening created by non-coincident axes of the shaft and ring. The flexible portion has a number of truncated conical panels with alternating orientation that accommodate the variable size opening by flexing in an accordion-like fashion.

TECHNICAL FIELD

This disclosure relates to the field of vehicle drivelines. Moreparticularly, the disclosure pertains to a constant velocity universaljoint having a protective shield.

BACKGROUND

FIG. 1 schematically illustrates a rear wheel drive vehicle powertrainwith an independent rear suspension. Solid lines indicate shafts capableof transferring torque and power. Engine 10 converts chemical energy inthe fuel into mechanical power. Transmission 12 modifies the speed andtorque to suit current vehicle requirements. At low vehicle speed, thetransmission provides torque multiplication for improved performance. Atcruising vehicle speed, the transmission increases speed permitting theengine to run at a fuel efficient operating point. The output oftransmission 12 is coupled to the input of differential 14 by reardriveshaft 16. Two components are coupled when rotating either componentby one revolution causes the other component to rotate by onerevolution. Differential 14 distributes the power to left rear wheel 18and right rear wheel 20 via left axle shaft 22 and right axle shaft 24respectively. Differential 14 changes the direction of rotation by 90degrees and multiplies the torque by a final drive ratio. Differential14 provides approximately equal torque to each wheel while permittingslight speed differences as the vehicle turns a corner.

In a four wheel drive vehicle based on the powertrain of FIG. 1, atransfer case fixed to the transmission divides power between the reardriveshaft 16 and a front driveshaft that directs power to the frontwheels via a front differential. In a front wheel drive powertrain, thefront differential is typically integrated with the transmission in anassembly called a transaxle. In a four wheel drive vehicle based on afront wheel drive powertrain, a power take-off unit fixed to thetransaxle drives a rear driveshaft and a rear drive unit fixed to therear differential selectively transfers power to the rear differential.Throughout this document, the term transmission should be interpreted toinclude any transfer case or power take-off unit. Similarly, the termdifferential should be interpreted to include any rear drive unit.

Engine 10, transmission 12, and rear differential 14 are mounted tovehicle structure. Wheels 18 and 20 are supported via a suspension thatallows the wheels to move vertically over road bumps while limiting thevertical movement of the vehicle body. The axis of rotation of engine 10and transmission 12 may be offset slightly from the input axis ofdifferential 14. Universal joints 26 and 28 accommodate this offset bytransmitting torque and power between shafts that rotate aboutintersecting but not coincident axes. Similarly, universal joints 30,32, 34, and 36 accommodate the offset between the output axis ofdifferential 14 and the axes of rotation of wheels 18 and 20 even thoughthe axes of rotation of the wheels fluctuates as the wheels absorb roadbumps. In some rear wheel drive vehicles, the differential 14 is notmounted directly to the vehicle frame but is instead supported by leftand right axles 22 and 24. This eliminates the need for universal joints30 and 34 but universal joints 26 and 28 must then accommodate afluctuating offset between the transmission output axis and thedifferential input axis.

A variety of types of universal joints are known. In the simplest typesof universal joint, although the driving shaft and driven shaft arecoupled, the instantaneous speed of the driven shaft differs slightlyfrom the instantaneous speed of the driving shaft as a function ofrotational position. Consequently, although the driving shaft may have aconstant speed, the driven shaft speed may oscillate at a frequencyproportional to the driving shaft speed. Due to the inertia associatedwith the driven shaft, this results in an oscillating torque level. Theoscillating torque level may be perceived by vehicle occupants,especially if the frequency is close to a natural frequency of thedriveline. Therefore, universal joints that maintain equal instantaneousspeeds between the driving and driven shafts, called Constant Velocity(CV) joints, are desirable. Several types of CV joint mechanisms areknown. Among known CV joint types, tripod joints and Rzeppa joints arecommon in automotive drivelines.

SUMMARY OF THE DISCLOSURE

A constant velocity joint includes a ring, a shaft, a flexible boot, anda protective shield. The ring is adapted for fixation to a flange of apowertrain component such as a transmission. The ring and the shaft arecoupled to rotate at the same rotational speed, but their axes are notconstrained to be coincident. The flexible boot seals a cavitycontaining lubricating fluid. The protective shield includes a rigidportion and a flexible portion. The rigid portion, which is fixed to thering, extends axially over the boot to protect the boot from projectilesand to prevent ballooning. An outer edge of the flexible portion isfixed to the ring while an inner edge of the flexible portion maintainscontact with the shaft, preventing projectiles from reaching theflexible boot around the rigid portion. The flexible portion may definea plurality of truncated conical panels with alternating orientationsuch that the flexible portion deflects accordion fashion to accommodatethe non-coincident axes of the ring and shaft. Both the rigid portionand the flexible portion of the protective shield may be formed inmultiple circumferential segments for ease of assembly.

A vehicle driveshaft includes a shaft, a ring, a flexible boot, a rigidshield, and a flexible shield. The shaft is adapted for fixation to adifferential at one end and is coupled to the ring at the opposite end.The shaft and the ring have non-coincident axes. A flexible boot isfixed to the ring and to the shaft. The rigid shield fixed to the ringextends axially over the flexible boot to protect the boot fromprojectiles and to prevent ballooning. An outer edge of the flexibleshield is fixed to the rigid shield while an inner edge of the flexibleshield contacts the shaft. The flexible portion may define a pluralityof truncated conical panels with alternating orientation such that theflexible portion deflects accordion fashion to accommodate thenon-coincident axes of the ring and shaft. Both the rigid portion andthe flexible portion of the protective shield may be formed in multiplecircumferential segments for ease of assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vehicle powertrain.

FIG. 2 is side cross section of a CV joint suitable for use in severallocations in the powertrain of FIG. 1.

FIG. 3 is an end cross section of the CV joint of FIG. 2.

FIG. 4 is a pictorial view of the CV joint of FIG. 2.

FIG. 5 is a side cross section of the CV joint of FIG. 2 with aprotective shield.

FIG. 6 is a pictorial view of the CV joint of FIG. 2 with a protectiveshield.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

FIGS. 2-4 illustrate a Rzeppa-type CV joint suitable for use at 26, 28,30, 32, 34, and/or 36 in FIG. 1. FIG. 2 is a cross section in the planedefined by the centerlines 50 and 52 of the two sides of the joint. Ring54 is adapted for fixation to the driveline component such as thetransmission output shaft, the wheel, or the differential as describedin detail below. Stub shaft 56 is adapted for fixation to driveshaft 16or to an axle shaft 22 or 24. Stub shaft 56 may be fixed to the shaft bywelding at the circumference of flange 58, for example. Six concavegrooves 60 are formed in ring 54 and six convex grooves 62 are formed instub shaft 56. Six balls 64, each positioned within a concave groove 60and a convex groove 62, position stub shaft radially with respect toring 54. The balls can roll within the grooves to accommodate the anglebetween axis 50 and axis 52. For example, as shown in FIG. 2, the ballat the top has rolled toward the left of the groove in ring 54 and hasrolled toward the right end of the groove in stub shaft 56. The ball onthe bottom has rolled the opposite direction. As either the ring or thestub shaft rotates about its respective axis, the balls force the othermember to rotate by an equal amount such that the grooves line up at theball locations. The balls may be retained by a cage (not shown).

Proper function of the joint requires lubrication, typically in the formof grease. A back plate 66 and a flexible boot 68 seal a cavity toretain the grease and to prevent contaminants from entering. Flexibleboot 68 may be a J-shaped boot fixed to front plate 72 which, in turn,is fixed to ring 54. Boot 68 is made of a flexible material toaccommodate the different axes of rotation. During each revolution ofthe shafts, a particular circumferential portion of the boot changesfrom the shape shown at the top of FIG. 2 to the shape shown at thebottom of FIG. 2 and then back. In some applications, such as theunderside of an off-road vehicle, the joint may be vulnerable toprojectiles that may puncture the J-boot. If the grease leaks out orcontaminants get in, friction may lead to rapid temperature increase andjoint failure.

Another failure mode, called ballooning, occurs when the pressure buildsup inside the grease cavity. This may occur, for example, due tofriction causing the temperature of the grease and air in the cavity toincrease. Centrifugal forces also contribute to internal pressure in thecavity. The increased pressure may cause boot 68 to deform such that theconvex surface facing the grease cavity becomes concave. This type ofdeflection weakens the boot material over time, eventually leading toloss of sealing function and eventual joint failure.

FIG. 3 is a cross section taken through the plane defined by the sixballs 64. FIG. 4 is a pictorial view of the joint. Ring 54 defines sixholes 70 that are used to fix the ring to the component, such as thetransmission, differential, or wheel. Specifically, six bolts areinserted through the holes 70, from the side with the J-boot, intothreaded holes in a flange of the component. Washers may be inserted todistribute the compressive force from the bolt head across the face ofthe front plate 72. In some cases, it may be necessary to rotate theshaft after inserting some of the bolts in order to be able to reach theremaining bolts with an appropriate tool. The shaft may be welded to thestub shaft 54 prior to positioning the shaft assembly into the vehicle.

FIGS. 5 and 6 show the CV joint of FIGS. 2-4 with a protective shield.FIG. 5 is a cross section in the same plane as FIG. 2. The protectiveshield includes a rigid portion 74 and a flexible portion 76. The rigidportion 74 is fixed to the ring. For example, the rigid portion may befixed to the ring by the same bolts 78 that fix the ring to thedriveline component. A flange of the rigid portion may be compressedbetween the washer 80 and the front plate. The rigid portion 74 alsoconstrains boot 68 from ballooning outward. The rigid portion protectsthe flexible J-boot from damage. The flexible portion seals off the gapbetween the rigid portion and the shaft, preventing any projectiles fromreaching the J-boot and potentially rupturing it. In order toaccommodate the non-coincident axes of rotation, an inner edge of theflexible portion must be capable of moving to a position not concentricwith an outer edge. This may be accomplished, for example, by formingthe flexible portion with an accordion shape having a number oftruncated conical panels 77 with alternating orientation. Unlike theflexible J-boot, however, the flexible portion of the protective shielddoes not need to form a seal against the shaft. If a projectile, such asa rock, creates a small hole in the flexible portion, the universaljoint will continue to function properly.

FIG. 6 is a pictorial view of the CV joint with protective shield 74 and76. FIG. 6 also shows the six bolts 78 and the washers 80 used to fastenring 54 to a component flange. Note that both the rigid portion 74 andthe flexible portion 76 of the shield may be formed from multiplecircumferential segments 82 which collectively surround thecircumference of the J-boot. Each circumferential portion can befastened to the CV joint separately.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A universal joint comprising: a ring having aring axis; a shaft coupled to the ring and having a shaft axisnon-coincident with the ring axis; a flexible boot fixed to the ring andto the shaft; a rigid shield fixed to the ring and extending axiallyover the flexible boot; and a flexible shield fixed at an outer edge tothe rigid shield and contacting the shaft at an inner edge.
 2. Theuniversal joint of claim 1 wherein the rigid shield comprises multiplecircumferential segments.
 3. The universal joint of claim 1 wherein theflexible shield defines a plurality of truncated conical panels havingalternating orientation.
 4. The universal joint of claim 1 wherein theflexible shield comprises multiple circumferential segments.
 5. Theuniversal joint of claim 4 wherein each circumferential segment definesa plurality of truncated conical panels having alternating orientation.6. The universal joint of claim 1 wherein an instantaneous rotationalspeed of the ring with respect to the ring axis is constrained to beequal to an instantaneous rotational speed of the shaft with respect tothe shaft axis at all rotational positions of the shaft.
 7. Theuniversal joint of claim 6 further comprising: six balls each configuredto roll within a respective convex groove in the shaft and within arespective concave groove in the ring.
 8. A vehicle driveshaftcomprising: a shaft having a shaft axis and adapted for fixation at afirst end to a differential; a ring adapted for fixation to atransmission and coupled to a second end of the shaft to rotate about aring axis non-coincident with the shaft axis; a flexible boot fixed tothe ring and to the shaft; a rigid shield fixed to the ring andextending axially over the flexible boot; and a flexible shield fixed atan outer edge to the rigid shield and contacting the shaft at an inneredge of the flexible shield.
 9. The driveshaft of claim 8 wherein therigid shield comprises multiple circumferential segments.
 10. Thedriveshaft of claim 8 wherein the flexible shield defines a plurality oftruncated conical panels having alternating orientation.
 11. Thedriveshaft of claim 8 wherein the flexible shield comprises multiplecircumferential segments.
 12. The driveshaft of claim 11 wherein eachcircumferential segment defines a plurality of truncated conical panelshaving alternating orientation.
 13. A constant velocity jointcomprising: a ring having a ring axis and adapted for fixation to aflange of a powertrain component; a shaft having a shaft axis notconstrained to be coincident with the ring axis, the shaft coupled tothe ring such that a rotational speed of the shaft and a rotationalspeed of the ring are constrained to be equal; a flexible boot fixed tothe ring and to the shaft to seal a cavity containing a lubricatingfluid; and a protective shield having a rigid portion fixed to the ringand extending axially over the flexible boot and having a flexibleportion fixed at an outer edge to the rigid portion and contacting theshaft at an inner edge of the flexible portion.
 14. The constantvelocity joint of claim 13 wherein the protective shield comprises atleast two circumferential segments each fixed to the ring by bolts and awasher.
 15. The constant velocity joint of claim 13 wherein the flexibleportion defines a plurality of truncated conical panels havingalternating orientation.